This invention relates to a vehicle traction control system.
Various methods have been proposed for preventing an excessive spinning condition of the driven wheels of a vehicle during vehicle acceleration when the operator initiated engine torque delivered to the vehicle driven wheels are such that the frictional forces between the tire and the road surface are overcome. These methods include the adjustment of engine torque and/or the application of the brakes of the driven wheels when an excessive acceleration spinning condition is detected. One method of adjusting engine torque output for limiting wheel spin during vehicle acceleration controls the individual injectors in a port injected internal combustion engine so as to selectively withhold fuel from selected cylinders. This disabling of cylinders reduces the engine torque output to limit acceleration spin. In general, the number of cylinders to which fuel is withheld determines the amount of reduction in the engine torque output.
In the foregoing form of traction control in which the engine output torque is reduced by selectively disabling engine cylinders, each cylinder disabled represents a relatively large reduction in the torque output of the engine. Typically, the first cylinder disabled usually produces the greatest power loss. As a result, on a dry road launch of the vehicle, the torque reduction provided by disabling one of the engine cylinders in response to a sensed excessive acceleration spin condition may be greater than the torque reduction necessary for control of the acceleration spin thereby resulting in less than optimum acceleration performance of the vehicle. Further, the large shift in power as the first cylinder is disabled may result in a perceived sag in the vehicle performance. Accordingly, it would be desirable to provide for a torque reduction level that is less than the torque reduction resulting from disabling one cylinder of the engine to accommodate acceleration conditions, such as a dry road launch, requiring a smaller torque reduction to arrest the excessive acceleration spin condition.
The amount of the torque reduction associated with disabling one cylinder of the engine may be reduced by creating "half" cylinder increments by disabling a given cylinder such as on every other engine cycle or even every third engine cycle. However, in practice this approach may produce rough engine operation due to the cylinder toggling on and off. It would be more desirable and result in smoother engine operation if the number of cylinders enabled during the traction control cycle remains constant or changes gradually.